c++ - Virtual visitor -

i have hierarchy of classes (base , daugthers a, b, c , on). hierarchy tree not finite. it’s possible visit base* using well-known visitor pattern in order dynamically adapt dynamic type of base*. visitor has type, basevisitor. this:

struct basevisitor;  struct base {   virtual void accept(basevisitor &v) = 0; };  struct : base {   int a;    a(int x) : a(x) {}   ~a(void) = default;    void accept(basevisitor &v) override {     v->visit(*this);   } };  struct b : base {   float b;    b(void) : b(314.f) {}   ~b(void) = default;    void accept(basevisitor &v) override {     v->visit(*this);   } };  struct basevisitor {   void visit(base &) {}    void visit(a &a) {     std::cout << "just visited a; a=" << a.a << std::endl;   }    void visit(b &b) {     std::cout << "just visited b; b=" << b.b << std::endl;   } }; 

now, i’d make basevisitor abstract class in order inherits new visitors. issue comes when want define abstract class:

struct abasevisitor {   virtual void visit(base &) = 0; /* huh? */ }; 

do have idea?